Oxygen consumption is increased relative to work rate in patients with McArdle's disease

• Published in: European journal of clinical investigation 2004-11, Vol.34 (11), p.731-737
• Main Authors: O'Dochartaigh, C. S., Ong, H. Y., Lovell, S. M., Riley, M. S., Patterson, V. H., Young, I. S., Nicholls, D. P.
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Blood Pressure - physiology; Carbohydrates (enzymatic deficiencies). Glycogenosis; Cardiopulmonary exercise testing; catecholamines; Epinephrine - blood; Errors of metabolism; Exercise Test - methods; Female; General aspects; Glycogen Storage Disease Type V - physiopathology; Heart Rate - physiology; Humans; Male; McArdle's disease; Medical sciences; Metabolic diseases; myophosphorylase deficiency; Norepinephrine - blood; Oxygen Consumption - physiology; Respiratory Function Tests - methods
• ISSN: 0014-2972; 1365-2362
• DOI: 10.1111/j.1365-2362.2004.01423.x

Background  Patients with McArdle's disease suffer exercise incapacity as a result of myophosphorylase deficiency, and for a given work rate have excessive circulatory and ventilatory responses. We hypothesized that the rate of increase of oxygen consumption with work rate (ΔVO2‐ΔWR slope) would also be elevated in such patients as a result of these excessive responses. Patients and methods  Five patients with McArdle's disease and five matched controls carried out a maximal incremental cardiopulmonary exercise test. Controls then carried out a second test matched to the maximal test of a paired patient. Venous blood was sampled at rest, peak exercise and recovery. Results  During the matched test, the ΔVO2‐ΔWR slope was higher in the patients than in the controls [19·9 (15·0–24·6) vs. 11·7 (9·2–13·5) mL min−1 W−1; mean (range); P = 0·022], and the peak‐achieved VO2 was also greater in the patient group [1201 (890–1575) vs. 918 (599–1248) mL min−1; P = 0·003]. A similar pattern was observed for heart rate [173 (165–182) vs. 108 (105–134) b.p.m.; P = 0·001] and plasma norepinephrine levels [12·6 (9·2–19·9) vs. 2·9 (2·2–4·9) nmol l−1; P = 0·003]. Conclusion  There is an increased rate of rise in VO2 relative to work rate during exercise in patients with McArdle's disease. There is also a greater rise in catecholamines, which may be the result of a physiological response to substrate starvation, and is likely to contribute to the increase in VO2.